This volume presents the contributions to the third symposium on the "Search for the Causes of Schizophrenia". The first symposium was organized by the Central Institute of Mental Health on the occasion of the 600th anniversary of the University of Heidelberg in 1986. Its objective was to give an overview of the rapid development in schizophrenia research in a situation characterized by an excessive variety of methods and topics. It was our intention, through substantial contributions to topical areas of schizophrenia research and through intensive discussions, to further the exohange of hypotheses and results and thus open up ways towards new concepts integrating different methodological approaches or towards new models of explanation. The first symposium was a great success. The publication of the proceedings (Hafner et al. 1987) was received with enthusiasm and recommended in leading journals "as the best available state-of-the-art analysis of current research on the aetiology of schizophrenia". For this reason we held a second and a third symposium entitled "Search for the Causes of Schizophrenia" under the same auspices and at the same place in 1989 and 1993.